Understanding of the interactions between azole-anion-based ionic liquids and 2-methyl-3-butyn-2-ol from the experimental perspective: the cage effect.

The interactions between azole-anion-based ionic liquids (AILs) and 2-methyl-3-butyn-2-ol (MBY) play an important role in AIL-promoted carboxylative cyclization of MBY with CO 2 . To better understand the interactions between AILs ([P 66614 ][Im], [P 66614 ][4-MeIm], and [P 66614 ][4-BrIm]) and MBY, a detailed investigation from the experimental perspective has been carried out in this study. The results show that the derivative of viscosity ( η ) with the mole fraction of AIL ( x AIL ) of AIL + MBY mixtures appears to have the maximum value when x AIL ≈ 0.3, while 1 H NMR chemical shifts of P-CH 2 of [P 66614 ] + reach the minimum value at x AIL ≈ 0.3, indicating that [P 66614 ] + of AILs tend to self-aggregate. The interaction parameters ( g ji - g ii ) of the systems obtained from η by the Eyring-UNIQUAC equation are positive, and the difference between the bulk and local composition ( x i - x ii ) is always negative, indicating that AILs can interact with MBY. Moreover, excess molar volumes and isentropic compressibility deviations are all negative deviations and become more negative as the temperature increases, reaching a minimum value at x AIL ≈ 0.30, indicating that azole-based anions can form H-bonds with MBY, and MBY molecules tend to enter the aggregates formed by AILs. Consequently, the cage effect is proposed to describe the interactions between AILs and MBY: MBY first enters the cage formed by the aggregation of [P 66614 ] + , and then forms H-bonds with azole-based anions. Finally, the sizes of the particles of the [P 66614 ][Im] + MBY mixture from dynamic light scattering increase first and then decrease with x AIL , with the maximum of 122 nm at x AIL ≈ 0.25, which confirms the rationality of the cage effect.